The Role Of Rab6 GTPase In Phagocytosis And Characterization Of Macrophages In Tumor Metastasis

Macrophages are an essential component of innate immunity and play a vital role in inflammation and host defense. Moreover, these cells exert homeostatic functions, including tissue remodeling and orchestration of metabolic functions. Cells of the monocyte-macrophage lineage are characterized by considerable plasticity and diversity. Based on immunological responses, the macrophages are classified into different subtypes. These include the "activated" macrophage (M1 macrophages) participating in the responses of type I helper T (Thl) cells to pathogens. This population is activated by interferon gamma (IFN-y) and lipopolysaccharide (LPS) and is characterized by the ability to kill cell and pathogens. However, the "alternatively activated" macrophages (M2 macrophages) differentiate in response to interleukin (IL)-4 and IL-13. These cells are involved in Th2-type responses, including angiogenesis and wound healing. Tumor associated macrophages are usually M2 phenotype. Hence, it is of great significance to study the role of heterogeneous macrophages in antimicrobial immunity and cancer progression.As professional phagocytes, M1 macrophages participate in antimicrobial immunity. Phagocytosis of M1 macrophages, an evolutionarily conserved process in animals, plays an important role in host defense against pathogen infection. As reported, Rab6 was involved in the regulation of hemocytic phagocytosis in invertebrates. However, the role of Rab6 in mammalian phagocytosis remains to be addressed. In this study, the results showed that Rab6 took great effects on phagocytosis in macrophages RAW 264.7 cells. It was revealed that Rab6 played an important role in the phagosome maturation by interaction with BICD1. Further data presented that the Rab6-regulated phagocytosis could inhibit the proliferation of Staphylococcus aureus in macrophages.Besides, tumor progression is controled by crosstalk between cancer cells and other cell types within the tumor microenvironment, including tumor cells, blood vessels, the tumor stroma, inflammatory cells and a variety of associated tissue-type cells. M2 macrophages in the tumor microenvironment not only fail to perform anti-tumour functions but are co-opted to promote tumor progression by releasing a variety of cytokines. However, the macrophage recruitment mechanism and the roles of macrophage-derived cytokines in tumor progression are largely unknown. The results of this study showed that M2 macrophage-secreted chitinase 3-like protein 1 (CHI3L1) promoted the metastasis of gastric and breast cancer cells in vitro and in vivo. The CHI3L1 protein functioned by interacting with interleukin-13 receptor a2 chain (IL-13Ra2) molecules on the plasma membranes of cancer cells. Activation of IL-13Ra2 by CHI3L1 triggered the activation of the mitogen-activated protein kinase (MAPK) signalling pathway, leading to the upregulated expression of matrix metalloproteinase (MMP) genes, which promoted tumor metastasis. The results of this study indicated that the level of CHI3L1 protein in the sera of patients with cancer was significantly elevated compared with those of healthy donors. Therefore, our study revealed a novel aspect of macrophages with respect to cancer metastasis and showed that CHI3L1 had the potential to be a therapeutic target for metastatic cancer.In order to explore whether shrimp miRNAs could regulate cancer metastasis by downregulating CHI3L1 expression level, we predicted the shrimp miRNAs targeting CHI3L1 gene. The analysis revealed that three shrimp-specific miRNAs (mja-miR-35, mja-miR-36, mja-miR-37) could potentially target human CHI3L1 mRNA 3’UTR. The results showed that overexpression of mja-miR-35 in M2 macrophages could decrease the expression level of CHI3L1 gene and the secretion of CHI3L1 protein, and the migration of cancer cells was influenced. However, mja-miR-36 or mja-miR-37 overexpression had no influence on CHI3L1 gene expression. Further data revealed that all of the three miRNAs could be loaded into AG02 proteins, indicating that the binding of mja-miR-36 and mja-miR-37 with AG02 protein might change the conformation of AG02 protein. This merited further investigation. Besides, the results of this study showed that mja-miR-35 was involved in the antiviral immune response in shrimp. Thus, our study revealed that shrimp-specific mja-miR-35 could simultanously regulate antiviral immunity in shrimp and cancer metastasis in human.In this study, we investigated the different functions of macrophages in antimicrobic immunity and cancer metastasis. The potential role of Rab6 GTPase in phagocytosis was investigated. The results showed that Rab6 was involved in phagosome maturation by interacting with BICD1. On the other side, the results presented that M2 macrophages could promote cancer progression. The data revealed that M2 macrophage-derived CHI3L1 protein could promote cancer metastasis by interacting with IL-13Ra2 on cancer cell membrane. The results of this study showed that shrimp-specific mja-miR-35 could regulate antiviral immunity in shrimp and cancer metastasis in human, thus providing evidence of cross-kingdom regulation by miRNAs. In this context, this study revealed new functional mechanisms of macrophages in antimicrobic immunity and cancer metastasis.